Note that the file ls-laR contains a list of all files accessible here.
The contents of some of the important directories under /pub/linux:
ALPHA Possibly dangerous alpha versions of software.
distributions/Debian The Debian distribution: large, solid.
docs WWW/html versions of Linux documentation.
Howtos The Howto documents
kernel The latest kernel sources are here.
MIPS The port of Linux to MIPS machines.
misc Odd files not found elsewhere in this directory.
packages Many packages are mirrored from tsx-11.mit.edu, including
GCC, TeX, X11, emacs, ingres, interviews, modula-2, oberon
sources A mirror of /pub/linux/sources from tsx-11.mit.edu.
standards Standards documents for Linux, including the file system.